In the manufacture of semiconductor devices and other ion related products, ion implantation systems are used to impart dopant elements into semiconductor wafers, display panels, or other types of workpieces. Typical ion implantation systems or ion implanters impact a workpiece with an ion beam utilizing a known recipe or process in order to produce n-type or p-type doped regions, or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects selected ion species to produce the desired extrinsic material. Typically, dopant atoms or molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and implanted into a workpiece. The dopant ions physically bombard and enter the surface of the workpiece, and subsequently come to rest below the workpiece surface in the crystalline lattice structure thereof.
In a conventional ion implantation system, a so-called “triode” design is utilized for extraction of an ion beam from an ion source, whereby a suppression electrode and a ground electrode are positioned in front of an opening of the ion source to extract the ion beam. The ion beam is subsequently analyzed by an AMU or mass analyzer magnet. With high extraction currents (e.g., so-called “high current implanters”), however, the ion beam will have a tendency to expand or “blow up” due to space charge, whereby individual ions of the ion beam tend to repel each other. When extracting a positive ion beam, for example, the positive ions repel each other due to electrostatic repulsion or space charge. Typically, residual gases are also present, thus creating secondary electrons that tend to neutralize the beam. However, in the extraction region, these secondary electrons get removed due to the strong electrostatic fields, thus preventing the beam from being neutralized. As such, the ion beam becomes larger and larger to the point that the whole ion beam can no longer be transported through the mass analyzer magnet, and gets clipped at the top and bottom of the ion beam.
As opposed to utilizing a triode design for extracting the ion beam, a “tetrode” design may be utilized, whereby a greater degree of flexibility is achieved. Referring initially to FIG. 1, a conventional tetrode extraction assembly 10 is illustrated, as disclosed in U.S. Pat. No. 6,559,454. The tetrode extraction assembly 10 comprises a housing 15 having an arc chamber 20A mounted thereto. A bushing 20B acts as an insulator to isolate a plasma source 20 from the remainder of the housing 15. Ions formed in the arc chamber 20A are extracted from the plasma source 20 through an exit aperture 21 in a front face of the source 20, therein defining a source electrode 22 at a source potential of the plasma source 20. Each of an extraction electrode 23, a suppression electrode 24 and a ground electrode 25, respectively referred hereafter as E-S-G, comprise conductive plates having a respective aperture therethrough to allow the ion beam 30 to pass and emerge from the ion source assembly 10.
For positive ion beams 30, for example, the ion source 20 is biased to a large positive potential (10-90 kV), whereby a final energy of the ion beam 30 is generally determined. The extraction electrode 23 is biased negative to the source potential associated with the source electrode 22 to extract ions from the plasma source 20, and the suppression electrode 24 is biased negative with respect to the ground electrode 25 to prevent electrons downstream of the ground electrode from back-streaming to the plasma source, and thus maintaining beam neutralization. The extraction electrode 23 is typically mounted on arms 43 to the plasma source 20 with an insulator 44 and is biased with a power supply with respect to the plasma source.
The conventional tetrode extraction assembly 10 uses three power supplies (not shown) and respective feed-throughs (not shown) to respectively power the source electrode 22, extraction electrode 23, and suppression electrode 24, whereby coating and/or electrical shorting may be experienced. Further, the conventional ion source assembly 10 may suffer from coating of the insulator 44 associated with the extraction electrode or other electrical shorting between insulators. Additionally, having four apertures associated with the source electrode 22, extraction electrode 23, suppression electrode 24, and ground electrode 25, respectively, various issues related to the alignment of all four apertures may be problematic.